Method of drying lumber.



No. 649,758. Patented May 15, I900. G B. ROBERTSON.

METHOD OF DRYING LUMBER.

(Application filed-Apr. 19, 1900.) (No Modem 4 Sheets-Sheet I.

No. 649,758. Patented May-l5, 1900. a. B. nosamson.

METHOD OF DRYING LUMBER.

(Application filed Apr. 19, 1900.) I

4 Sheets-Sheet 2.

(No Model.)

w Inventor- L go I g N' 01y No. 649,758. Patented May l5, I900. G. B.ROBERTSON.

METHOD OF DRYING LUMBER.

(Application filed Apr. 19, 1900.) (No Model.) 4 Sheets-Sheat 3.

THE NoRms PETERS c0. pnoro umou WASHINGTON. n. c

Patented May 15, I900.

G. B. ROBERTSON.

METHOD OF DRYING LUMBER.

(Application fileApr. 19, 1900.)

V 4 Sheets-8heet 4.

(No Model.)

ls PETERS co, vnorc-uwo, WASHINGTON. u c.

rich.

GEORGE B. ROBERTSON, OF IVHALEYVILLE, VIRGINIA.

METHOD or DRYING LUMBER.

SPECIFICATION forming part of Letters Patent No. 649,758, dated 15,1900.

Original application filed December 23, 1897, gerial No. 663,211.Divided and this application filed April 19, 1900- Serial No.

13,499. (No specimens.)

To all 2107mm, it may conceive:

Be it known that LGEORGE B.ROBERTSON, a citizen of the United States,residing at Nhaleyville, in the county of Nansemond and State ofVirginia, have invented certain new and useful Improvements in Methodsof Drying or Seasoning Lumber, of which the following is aspecification.

My invention consists in a novel method of drying or seasoning lumber,the peculiar features of which will be set forth in the followingdescription.

The accompanying drawings illustrate the construction of a kiln suitableor convenient to the carrying out of the process, which kiln will befirst described, after which the method or process will be explained.

Figure l is a perspective View of a series of kilns built side by side,with a view to bandling large quantities of lumber and maintaining someportion of the plant always in operation. Fig. 2 is a vertical sectionalview through one kiln or chamber from end to end, portions being removedto permit the struc' ture to be shown on a reasonably-large scale andother parts being broken away to expose the steam-pipes; Fig. 3, ahorizontal section on the line as of Fig. 4; Fig. 4, a Verticalcross-section of one kiln or chamber; Fig. 5, a detail of thecurtain-fastenings; Fig. 6, a diagrammatic perspective illustrating thearrangement of the horizontal fines for escape of moisture and relief ofpressure within the kiln; Fig. '7, adiagram illustrating the steamcirculation; Fig. 8, a view illustrating a modification of thesupportingrolls.

As hitherto commonly constructed dryingkilns for lumber have beenprovided with a system of fines more or less elaborate designed toeifect a circulation of aircurrents within the drying-chamber. So far asI am aware all kilns hitherto constructed have been provided with meansfor introducing or admitting air from without and causing it tocirculate through the chamber,either throughout the entire dryingoperation or at some stage therein, and it has also been the usualpractice to provide means for withdrawing the moist air from thechamber. In order to provide space for the fines, it has been thegeneral practice to construct such kilns of wood,

which, however, is not only very liable to do struction by fire, but issubject to rapid de terioration. Under my plan of construction flues arewholly dispensed with throughout the structure, except that in somecases horizontal pipes or fines are carried from just below the roof ofthe structure to the outside to permit escape of moisture from and toprevent undue pressure within the dryingchambers. These flues may, ifpreferred, be omitted.

Referring again to the drawings, 1 indicates a substantial structureeonsisting,essentially-, of a roof and a series of parallel verticalwalls, the number of which will vary according to the number of kilns orchambers desired. If a single chamber is wanted, there will of course bebut the two walls, though it is deemed advantageous to employ a seriesof such chambers side by side. The walls are preferably placed fromnineteen to twenty feet apart to accommodate the ordinary lengths oflumber and allow space between its ends and the walls of the chamber forthe convenientpassageofattendants. Thespace is, however, a matter ofoption, variable according to the conditions of any given case. So, too,the height of the chambers above the runways over which the lumber ismoved may vary as desired, though I find a space of about twelve feet toanswer well ordinarily.

The walls are connected at top by a roof of any suitable construction.

\Vithin the chambers and extending outward therefrom at each end arerunways for the lumber, and these have a fall of about one foot infifty, more or less, as found expedien t. The runways consist of metalbeams or girders 2, arranged in pairs and held apart by spacing-blocksor otherwise, with wheels or rollers 3 placed between and projectingabove the beams, as seen in Figs. 1, 2, and 4-. \Vhile the measurementsare not important, but may vary as occasion may require or sug gest, Ihave found it convenient to employ channel-iron beams of about sixinches depth, spaced about four and a quarter inches apart, and to makeuse of grooved wheels of ten inches diameter, with a flange extendingradially about a half-inch farther. Such wheels are well suited toreceive and support T-rails 4, which I find it convenient to employ andto place in an inverted position, with their treads lying in the groovesof the wheels and spanning or bridging from one wheel to another, asindicated in Figs. 1 and 2. The wheels are conveniently made to turnfreely upon axles 5, resting upon the flanges of the beams 2 and firmlyclamped thereto by U- bolts 6, as shown in Figs. 1, 2, 3, 4, and 8; butthe axles may of course turn in bearings, if preferred. Obviously angleor channel irons may be used at will and of any desired dimensions. Theaxles may be set at such distances apart as found advisable, twentyinches being a suitable distance under ordinary conditions, and with therails 4 cut to a length of six feet. These measurements are, however,merely suggestive, being those which I have found satisfactory inpractice.

The beams or girders 2 are carried upon walls 7, extending lengthwise ofthe dryingchambers and preferably constructed as illustrated in Fig.3that is to say, with a series of piers 8 at convenient intervals, sayeight feet from center to center, connected bya wall of a singlethickness of brick, with bricks omitted at intervals to leave openings9. I have found it convenient to employ three runways, and consequentlythree such walls, one at the middle of the chamber and the others aboutsix feet therefrom and on opposite sides measuring from center tocenter; but this dis tance may vary.

It is desirable to give sufficient slant to the runways to facilitatethe movement of the lumber piles over them. Hence I give to the wallsand runways an inclination from the receiving end downward toward thedelivery end of approximately one foot in fifty. In the kilns actuallyconstructed the chambers have been one hundred and ten feet inlength andthe fall two feet, which is, found quite satisfactory.

At the ends of the chambers cross-walls 10 are constructed of the sameheight as the walls 7 at the respective ends, thus closing and sealingthe chambers from the groundline to such height.

Heretofore it has been customary to employ vertically-movablecounterbalanced doors arranged like window-sash for closing dryingkilns.Such doors are unsatisfactory for the reason that they cannot be closelyfitted and yet run freely, but are liable to warp and twist, andconsequently to bind or to draw away from the faces with which they aredesigned to move in contact. Moreover, they necessitate the applicationof considerable force to raise and lower them and the employment ofbooks or other means to start them downward when elevated. To obviatethese objections and insure an efficient sealing of the chamber, which Ideem important, I provide each opening with a curtain 11, of canvas,rubber cloth, asbestos, or other suitable material, painted, coated, orotherwise treated, if need be, or left in its natural condition. Canvas,well painted or filled, rubber cloth, and asbestos have all been triedby me 'with good results, canvas being perhaps the most satisfactory.The manner of hanging and controlling said curtain may vary, any usualway of arranging heavy curtains being available. In the drawings I haveshown the curtain firmly secured along its upper edge to the facing 12of the kiln, directly across the top of the opening, and I carry ropesor bands 13 down on one side and up on the other side of the curtain,thence over pulleys 14, and finally to a cleat 15 or other place offastening. By drawing in or paying out the bands or ropes the curtainmay be quickly and easily raised or lowered, a roll 16 at the lower edgeserving to insure its properwinding and unwinding. To make the curtaintight at its sides, I pro vide means for clamping its side edges fromtop to bottom. This may be done in a variety of ways; but I find itconvenient to provide the edges with eyelets or gromets 17, which areengaged over pins or studs 18, projecting from the facing-strips of thewalls, as seen in Figs. 1 and 5. To insure retention of the eyelets uponthe studs or pins, I provide cover-strips 19, which may conveniently behinged to the facing-strips and arranged to close over the ends of thestuds or pins, as shown in Fig. 5, where they may be secured byturn-buttons 20 (also shown in said figure) or by any equivalent means.

The roller frames or girders 2 are cutaway or set back sufficientl y ateach end of the kiln to permit the curtain to drop to or below the lowerline of the kiln-opening to insure its perfect closure.

It is desirable that means be provided for escape of moisture from theinterior of the kilns, though it may not be desired to utilize suchmeans at all times. To afford such outlet, I provide pipes 21, which arecarried from the outer wall inward to different distances, asillustrated in Fig. 6, each pipe terminating within and at or about themid-Width of one or another kiln or chamber. Such pipes may be repeatedat intervals, if desired, Fig. 1 showing three sets. The pipes or fluesextend horizontally and are located just beneath the roof, as indicated.To prevent wind or rain from driving into the pipes, their outer endsmay be provided each with a bend or elbow and, if desired, with a shortlength of pipe. By arranging the elbow to turn upon the horizontal pipethe outlet may be raised or lowered, and thus the resistance offered toescape of vapor from within the kiln may be varied as desired. I havethus far found in practice, however, that the pressure from within issuiiicieut to exclude wind and rain and that it is only necessaryordinarily to extend the ends of the pipes through the wall without bendor elbow of any kind. The number and size'of the pipes will beproportioned to the size of the kiln and the character of the lumbertreated and will ordinarily be IIO sufficiently small to insure themaintenance of pressure within the kiln.

\Vithin each kiln or chamber there is provided a system of steam-pipes22, which pipes I find it desirable to arrange between the roller framesor girders, as in Figs. 2 and 3, givingthem about the same fall, andthus insuring proper flow of the water due to con densation. Thearrangement of the pipes is open to variation; but I find it quitesatisfactory to employ at the receiving end a box or casting 23 at orabout the level of the inlet end of the pipe system, with which connectsa pipe 29 from the source of steanrsupply. The pipes 22 extendlengthwise of the drying kiln or chamber, as indicated in Figs. 2, 4,and 7, and at the delivery end of the kilns drop down to aseoond box orcasting 2%, which is in turn connected with the feed-water well or tankor with the feed-water heater 25 by a pipe 26, as indicated in Fig. 7.The pipes are preferably arranged in tiers one above another, theirnumber and size depending upon the requirements of the particular case.7

In Fig. '7 I have represented diagrammatically the preferred arrangementof' the plant whereby to utilize the exhaust-steam of the engine of themill for afiording heat in the drying-kiln. and to return the steam tothe feed-water heater for the purpose of heating the water therein or toreturn the condensed steam to the feed-water reservoir or well, so thatit may be fed into the boiler at a relatively-high temperature.

27 indicates a steam boiler or generator, 2 a stationary engine suppliedtherefrom, and 20 a pipe connecting the exhaust-port of the engine withthe head or casting 23 of the steampipe system in the kiln. From thehead or casting 24 at the foot of the steanrpipe system the pipe 26passes to the feed-water well or tank 30, whence it may be delivered bya pump 31 directly to the boiler 27 or to the feed-water heater 25, forwhich suitable pipes and valves are provided, or it may pass by a pipe(indicated by dotted lines in said figure) directly to the feed-waterheater. In this way I am enabled to utilize very fully the heat units ofthe fuel employed in generating steam, it being found in practice thatafter making the complete circuit the steam returns with heat sufficientto bring the feedwater to a temperature above 200, and, in fact, verynear to the boiling-point.

The kiln being constructed as above set forth is supplied with lumberhyplacing the rail lengths or sections 4 in an inverted position upon thewheels 3 and piling the lumber thereon in tiers or layers, eachseparated from the next by the usual separatingstrips 32. I'Ieretoforeit has been found necessary to place such strips at the extreme ends ofthe boards or planks, as well as at intervening points, five of suchseparating-strips being usually employed. Under my mode of treatment itis found unnecessary to employ so many strips, and the extreme ends maybe left wholly unsupported by such strips, and the number used may bereduced to three, of which there is one over each rail t, as shown inFig. 1. The rails being six feet in length, preferably, and the kilnhaving the clear height of about eleven feet, the lumber may be piled toa height of ten :feet, more or less, and yet travel freely through thekiln. The size of the lumber-piles is, however, optional and may bevaried at will. As the piles are completed the curtain at the receivingend is raised and the pile is rolled forward into the kiln and leftfirst at the receiving end and just within the chamber where the heat isgreatest, owing to the fact that the steam enters at that point. Asfresh piles are formed those previously introduced are moved backwardinto the kiln, and so on until the kiln is full or until as many pilesare introduced as deemed expedient. The length of time that the lumberis subjected to the heat will vary according to the character and thecondition thereof; but owing to the fact that a walk 33 is providedthroughout the length of each kiln or chamber, being supported uponcross rails or girders 34, extending from the main walls to the wallswhich support the roller-frame, the attendants may at any time go intoand through the kiln and examine the lumber therein.

Practical use of the process has demonstrated that it possesses many andimportant advantages over the ordinary methods of dryin g lumber. Amongthese may be mentioned the fact that the shrinkage of the lumber underthis mode of treatment is materially less than under the ordinary mode,never exceed ing fifty per cent. of the shrinkage heretoforeexperienced. The lumber when dried to the full extent required isheavier and the wood is left with more life and spring, works better,and is stronger than lumber treated in the ordinary way.

It is well known that kiln-dried lumber is often spongy and dead,causing great difficulty in working under the plane and not affordingthat smooth hard surface obtainable with lumber seasoned in the old wayand without the use of heat. Lumber treated by my process is found toretain its desirable properties, and it is further found that if takenfrom the kiln and exposed to the air before it is completely dried itdoes not blacken, as does lumber treated in ordinary kilns. Pitch pine,or so-called fat wood or light wood is treated with peculiar benefit inthis kiln. It is found that a considerable portion of the rosin isbrought to the surface and dried off, while another considerable portionis retained in the wood; but in no case does it drip from the ends ofthe boards to those beneath, as has invariably happened with kilns ofprior construction. This dripping of the rosin has been a very seriousdifficulty, since it spoiled the boards upon which it fell or reducedthem from one to two grades be low what they would otherwise have been.It is also found that boards treated by my process do not warp or checkat the ends and that the knots are left tight in the lumber, Whereasunder ordinary methods of treatment in kilns the knots are loosened andfall out, thus again decreasing the value of the lumber. These factshaving been definitely ascertained by practical use on a large scale andfor a considerable period of time and being obtainable from thedescription and explanation above given, it is not deemed necessary toset forth the theory upon which the differences in result rest. It is mybelief, however, that the vaporization of the moisture in the wood bythe heat Within the chamber and the pressure due to the vapor soproduced contribute to carry off the watery particles contained in thelumber without eliminating the resinous and other substances containedin the pores of the wood. It is found, however, that the wood isthoroughly seasoned to the center and that those boards which areimmediately above the steam-pipes are not impaired by their proximity tosaid pipes, nor are those at the top unseasoned or insufficientlytreated by reason of their being farther removed from the pipes.

For the various reasons above stated the construction and the mode oftreatment are highly advantageous as compared with the best kilns andsystems of drying with which in a wide experience in this field of WorkI have become acquainted.

In Fig. 8 there is shown a modification of the rollers and rail-sectionorlumber-support, the roller being in this case without flanges and therail or lumber-support being in the form of a channel-iron bar.

The mouths of the pipes 21 may be closed by plugs, dampers, orotherwise, either at the inner or the outer ends of the pipes, toregulate the escape of vapor from the chamber, it

being desirable to maintain at all times a certain amount of pressurewithin the chamber and upon the lumber, said pressure apparentlycontributing materially to the attainment of the results herein setforth.

The flexible curtains yield to a considerable degree to the internalpressure occasioned by the vapor given ofi by the lumber and tend toequalize the pressure and the consequent rate of escape of the vaporfrom the kiln. It is found in practice that the curtains are almostconstantly bulged outward in greater or less degree, thereby indicatingthe existence of pressure from within, to which pressure is due theelimination or discharge of the moistureladen vapor.

This application is divided out of an earlier application, Serial No.663,211, filed in the Patent Oflice on the 23d day of December, 1897,which parent application originally embraced both the method and theapparatus. The division is made in compliance with the requirement ofthe Office, and with the existing rule and practice.

While the above-described apparatus is peculiarly well adapted to thecarrying out of the process hereinbefore set forth, it is to beunderstood that said apparatus is the subjectmatter of a separateapplication for patent and that it is shown and described herein merelyfor convenience of illustration and not as indicating its necessary useas a means of carrying out the method or process herein claimed. Inother words, it is to be understood that the apparatus may be varied inform without in any manner departing from the scope or spirit of theinvention herein claimed. This method is not dependent upon this or anyother precise form of kiln, but may be practiced in any form of kilnfound suited thereto.

Having thus described my invention, what I claim is 1. Theherein-described method of treating lumber, which consists in subjectingthe same to the action of heat in a chamber closed against the admissionof the external atmosphere, and thereby vaporizing the moisturecontained in the lumber, and permitting the vapor thus produced toescape from the top of the chamber under regulated pressure,substantially as and for the purpose set forth.

v 2. The method of treating lumber, which consists in piling the same inseparated tiers or layers; placing the piled lumber in a chamber closedagainst entrance of the external atmosphere; subjecting the lumber whilein said chamber to heat and thereby vaporizing its moisture; maintainingthe heat until the requisite amount of moisture is driven out of thelumber; and permitting the vaporized moisture to escape from the upperpart of the chamber under regulated retardation, substantially as andfor the purpose set forth.

3. The method of treating lumber which consists in subjecting the sameto the action of heat in a chamber closed against admission of theexternal atmosphere, and having restricted escape for vapor at the upperpart of the chamber, whereby the moisture is driven from the lumber anda pressure is created within the chamber and upon the lumber,substantially as set forth.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

G. B. ROBERTSON.

Witnesses:

R. H. ROBERTSON, H. E. BRITTINGHAM.

IIO

